The present invention relates to methods and devices that employ electromagnetic radiation for measuring a level of a material in a receptacle. In particular, the present invention relates to a device for feeding microwave signals from different microwave channels to one antenna unit in a radar level gauging system. The invention further shows a method for achieving the feeding.
It is known to measure the level of the surface of a medium stored in a tank utilizing a radar level gauge. Such a device is described in U.S. Pat. No. 4,665,403. When measuring the level of the medium in a tank, there are often requirements that the level must be supervised to fulfill security restrictions. Hence, as an example, one or two independent overfill alarms must be installed. The user further may want redundancy in measured values which may require more than one installed measurement system, which may require at least two complete independent level gauges.
The desire for independence in the measurement system can extend to independent electrical circuits and cabling. That is, the system can include circuits and cabling without any galvanic contact between different measuring systems. However, fixed mechanical constructions for example, which cannot normally go wrong, may be shared. Float sensors and different types of capacitive sensors, for example, mounted in separate tank bushings are often utilized as sensors for such alarm systems. However, these sensors can be sensitive to linings, corrosion and other influence from the content of the load tanks or their wiring and the risk of malfunction is therefore evident.
Published international patent publication PCT/SE00/01291 discloses a device and a method for measuring the level of the surface of a medium in a tank. The disclosed device utilizes more than one radar channel to obtain a measured value of the level, where the level values measured in the channels are obtained independently of each other. This is accomplished by utilizing at least two microwave signals distributed in separate channels fed to the same antenna unit, whereby the at least two signals are used to measure the level independently of each other. The microwave signals can be distinguished utilizing a detectable characteristic.
Security restrictions to fulfill safety and environmental laws and requirements may result in a need for each measurement of the surface level of the medium in the tank to be completely separated from each other. It is often necessary to use two or more independent measurement instruments in order to make it possible to have the measurements regarded as fail-safe.
The present invention provides a liquid level measuring gauging system. The system includes a radar antenna. The system also includes a plurality of functionally independent radar measuring channels. A feeder is operably connected with the channels and operable to feed microwave signals of the channels to the antenna.
Also, the present invention provides a liquid level measuring gauging system. The system includes a radar antenna. A first radar-measuring channel is connected to the radar antenna and includes a transmitter, a receiver and an indicating element. At least one further radar-measuring channel is connected to the radar antenna. The radar waves of the further radar measuring channel are distinguishable from the radar waves used in the first radar-measuring channel.
Additionally, the present invention provides a liquid level measuring gauging system. The system includes an antenna unit. A feeder is operable to feed at least two distinguishable microwave signals to the antenna unit. The feeder includes at least two waveguide members. Each waveguide member is operable to receive one of the microwave signals from a transmission line. A plurality of functionally independent channels are operable to distribute the microwave signals. A plurality of transmission lines are operable to forward the microwave signals of the channels to the waveguide members of the feeder. A common waveguide outlet for all waveguide members is arranged at a waveguide interconnection.
Furthermore, the present invention provides an antenna feeder that includes at least two waveguide members each operable to receive a microwave signal from a transmission line operable to forward the microwave signal from one of a plurality of functionally independent channels to the waveguide members. A common waveguide outlet for all waveguide members is arranged at a waveguide interconnection.
Still further, the present invention provides a method for measuring level in a receptacle. The method includes distributing a plurality of distinguishable electromagnetic signals in separate channels. Each signal is fed to a separate waveguide member. The signals are transmitted from each waveguide member to a common outlet.
Also, the present invention provides a method for measuring a level in a receptacle using radar. Electromagnetic waves are transmitted with radar measuring channels via a single aerial directed down into a receptacle. The waves are distinguishable by a detectable characteristic for each channel. A reflected time-delayed wave is received. A level is calculated from the time delay.
Additionally, the present invention provides a method in a level measuring gauging system for feeding at least two distinguishable microwave signals distributed in separated channels to the same antenna hardware. A waveguide member is provided for each microwave signal. Each microwave signal is forwarded to an associated waveguide member through a transmission line associated with the signal. The transmission line is galvanically isolated from the associated waveguide member. The signals are transmitted from each waveguide member via an outlet common for all waveguide members.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from a review of the following detailed description. The detailed description shows and describes preferred embodiments of the present invention, simply by way of illustration of the best mode contemplated of carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the drawings and description are illustrative in nature and not restrictive.